Process of making chemically pure benzene



b. 19, 1935. R. w. CAMPBELL ET AL r 1,991,844

PRQCESS `01"' MAKING CHEMICALLY PURE BENZENE Filed June 7, 1934 INVENTOR Piensa Feb.19, 193s j I 1,991,844

UNITED' PATENT ori-ICE PROCESS F MAKING CHEMICAILY PURE BENZENE Robert W. Campbell and Fred W. Wagner, Pittsburgh, Pa., assigner: to Jones la Laughlin Steel Corporation, Pittsburgh, Pa., a corporationA o! Pennsylvania Application June 7, 1934', Serial No. '129,438 1s cmmr. (ci. 26o-19s) This invention relates'to the renning of intion benzene" are isolated and combined as a v dustrial pure benzene with the removal of im-4 separate product from the main distillate. Nitrapurities which are usually presentin ordinary tion benzeneis the usual trade name for benzene grades of benzene and whose presence seriously whose purity is such as to be acceptable-to the 5 affect the efficient production and quality of machemical industry for the production of phenol 5 terials producedby the chlorination or nitration or nitro-benzene. It is identled by having a i of benzene. freezing point of at least 5.0 C., a distillation The present application is a continuation-inrange of 1.07 C., a Bromine Index of not over part of our copending application Serial No. No. 10 and a specicgravity of at least .8820

10 676,134,111edJune16, 1933. (15.5 c./15.5 CJ. .The true freezing point of 10 By industrial pure benzene we mean that spebenzene is usually accepted as 5.5 C.' and the cie distillate produced by the refining of light specific gravity as .8850 (15.5 C./15.5` C.).

oil which is a coal-tar distillate. According to Our process deals with the production of nitrapresent practice, industrial pure benzene is protion benzene from industrialv pure benzene, the

. l5 duced by the washing of the crude light oil or purity of which is far superiorto any material 15 one of its fractions with sulphuric acid of 66 B. heretofore obtainable. By our process we can strength (93.19%) or less, in various'stages and produce, in a commercial manner, benzene that amounts, drawing oif the sludge formed thereby, has a freezing point of 5.4 C., a specific gravity neutralizing the product, and subjecting the of'.8838 and aBromine Index of No. 3. The distillation. By industrial pure benzene we mean of obtaining a yield of approximately 3S is. that fraction which distills, vaccording to the customary in the refractionation of industrial standard distillation test, within a 2.0 C. range pure benzene, we obtain, by our process, a conand which includes the true boiling point of bensistent yield of 80% to 85%.

25 zene (80.2 C.) Our process, which is based upon the principle 2.5

The benzene produced in this manner contains of fractional crystallization by freezing, embodies objectionable impurities such as carbon bisulnew technique in the art of separating benzene phide, thiophene and -parain hydrocarbons. from its impurities. As stated previously, it is These impurities are identified most readily by'v known that benzene may be, to. some limited ex- 0 their influence on the specific gravity and freezing tent, separated from its homologues, asdisclosed 30 point as well as the distillation range of the benby Manseld in ChemicalSociety Journal of Lonzene. The thiophene is identified by its reaction' don (Quarterly Journal) vol. 1," (1849) pp. 256- With isatin in the presence of sulphuric acid. 261., by the application of freezing. It is generally Benzene'may also be refined by freezing the known that, when benzene freezes inthe presence benzene and separating it from its impurities by of its impurities, relatively large amounts of these pressure and filtration. By this method, the benimpurities, which have a lower freezing point, are zene distillate is frozen and large quantities of entrained in the solid frozen mass. In the case impurities are entrained in the frozen benzene of freezing industrial pure benzene vwhich conwith the result that a poorer grade of benzene is tains relatively small amounts of impurities but 4 4pioducedjhan byfractional distillation. This of suicient quantity as to render it unflt for method of refining has never, heretofore, been the production of phenol or nitro-benzene, practicommercially employed because the product procally no separation is obtained by the method disduced by fractional distillation has been far suclosed by Mansfield or any other freezing method perior in quality. The separation of benzene from known to the art of benzene renning.

relatively small quantities .of impurities such as Our process prevents the impurities from being 45 parafn hydrocarbons in the boiling range of entrainedinthe frozen mass and, accordingly, the benzene, carbon bisulphide and thiophene, by the impurities are segregated in liquid form in the application of freezing or orystallizing the bencenter of the frozen mass of benzenel and are zene, has heretofore been considered unsatisfacdrawn off in a simple manner. We employ a very washed and neutralized product to fractional distillation range is approximately 0.5 C. Instead 20` tory in the art 0f refining. carefully controlled rate of freezing while the ma- 50 The usual method of producing benzene, known terial being frozen is in constant agitation. By to the trade as nitration benzene is to redistill such a procedure, it. is believed the benzene industrial pure benzene and, by careful fractionmolecules are so compressed that it iS impossible ation, certain receiversl of the distillate, which to entrain any of the impurities and a benzene 5 conform with the usual specifications for ninaalmost theoretically pure is obtainable by simply 55 drawing oil' the impurities as a liquid. The frozen benzene is then preferably melted and separated in a liquid form, or it may be removed from the freezing apparatus i'n solid form.

The accompanying drawing illustrates in a somewhat diagrammatic manner an apparatus suitable for carrying out our process.

Referring more particularly to the accompanying drawing, the industrial pure benzene containing carbon bislrilphide, thiophene and paraiiin hydrocarbons is charged into a freezing apparatus indicated by the reference'numeral 1. The freezing apparatus comprises an inner vertical metal container or can 2 and an outer jacket 3 provided with an inlet pipe 4 and valve 5 and an outlet pipe 6 and valve 7 for the cold brine from the main brine cooling and circulating tank. The. outer jacket 3 isvalso provided with an -outlet pipe. 8 and cock 9 and an inlet pipev l0 and cock 11 for controlling the circulation of the brine through the pump 12 and the heater 13 in order to warm the brine sufficiently to melt the benzene crystals after the liquid impurities have been withdrawn from the container 2. The container 2 is provided with an air p ipe 14 and valve 15 for controlling the air supply used for agitation during the freezing process. The container 2 is also provided with a main drain pipe 16 and valve 17 connected to the pipe 18 controlled by valve 19 for the removal of the liquid impurities, and to the pipe 20 controlled by valve 21 for the removal of the melted benzene crystals. The'following is a specific description of one manner of carrying out our process. i

' Industrial pure benzene having a boiling range of 2.0 C. (79.5 to 81.5 C.) containing impurities such as carbon bisulphide, thiophene and paramn hydrocarbons,. which .may be produced according to present practice by washing the crude light oil or one of its fractions with sulphuric acid of 66 B.' strength (93.19%) orless.

in various stages and amounts. drawing on the sludge formed thereby,- neutralizing the product, and subjecting the washed and neutralized product to fractional distillation, is charged into the freezing apparatus indicated by the reference numeral 1. It is preferred, however, where the crude light oil used in making the industrial pure benzene contains substantial amounts of sulphur containing hydrocarbons, for example carbon bisulphide and thiophene, to subject the crude light oil to the acid and distillation treatment described in our above referred to application Ser. No. 676 134, The process described in that applicationv consists briefly in treating the crudelight oil with sulphuric acid of 66 B. strength or less, drawing oif the sludge, neutralizing Athe product, subjecting the washed and neutralized product 'to fractional distillation,

treating the distillate with sulphuric acid of over 94% up to 100% strength.drawing oir the sludge, neutralizing the product, and subjecting the washed and neutralized product to fractional distillation. 'I'he industrial pure benzene thus produced -and having a boiling range of 2.0 .C. (79.5to 81.5 C.) is then subjected to fractional crystallization.

The industrial pure benzene is charged into a numberY of containers or cans); measuring six such vcontainers comprising one compartment, being equally spaced inside of an outer jacket 3 in order to allow the brine to circulate freely around the containers. Each' container is purities in the frozen benzene.

zene or 1,162 gallons in a twenty-eight container compartment of 1,494 gallons in a thirty-six container compartment. Usually four such com-v partments are connected with a brine cooling tank containing a refrigerating coil, by means of the inlet pipes 4 and valves 5 and the outlet pipes 6 and valves 7.

When the containers 2 are charged with industrial pure benzene, the inlet brine valve 5 and the outlet valve 7 are open and brine having a temperature between -4 C. and 15 C. and .preferably at an average temperature of 9 C. is in constant circulation around the containers 2. Immediately after charging the. benzene, the inlet air valve 15 is opened and the benzene is constantly agitated throughout the freezing cycle with air at approximately 3% pounds per square inch pressure.

We prefer to freeze at an average rate not to exceed 5% per hour during the freezing cycle or period. If this rate is materially exceeded, there is danger of entraining too much of the imratus described, the freezing cycle is completed in approximately thirty-nine hours.

l When the cycle of freezing'is completed, the air valve 15Ais closed and the liquid core of impurities is drawn off by gravity from the containers 2 by opening the valves 17 and 19.

After closing the valves 1'7 and '19, the cold brine around the containers 2 is cut olf from. the brine cooling tank-by closing the valves 5 and 7. The brine cocks 9 and l1 are now opened and the cold brine surrounding the containers 2 is pumped bymeans of pump 12 through the pipe 8 to a brine heater 13. By means of indirect steam the brine is heated to the proper tempera.-

around the containers 2 through the pipe 10. In

this manner the benzene crystals are melted by With the appathe warm-brine circulating around the containers 2. The temperature of the brine isv thermostatically controlled not to exceed-27 C. and the melting cycle requires approximately six hours.

When all of the benzene crystals have been melted the pump 12 is shut down and the brine cocks'\ 9 and 11 are closed. The chemically pure benzene is drawn off by gravity from the containers 2 by opening the valves 17 and 2l.

The valves 17 and 21 are then closed and the brine circulation to the brine cooling 'tank is resumed by opening the valves 5 and 7 and the containers 2 are again charged with industrial pure benzene.

We prefer to subject to fractional crystallizacrystallization as described. The'materlal to be subjected to fractional crystallization should,

' however, contain at least 90% pure benzene.

' Any suitable freezing medium can be employed in freezing thebenzene in place of the brine solution.

Instead of using air for agitating the benzene during freezing, any other suitable gas may be employed or we may use mechanical agitation. In the latter case, a stlrrer of small diameter freezing of the benzene onthe walls yof the con-v tainer 2.

We have described in detail the present preferred manner of practicing our invention and have illustrated diagrammatically an arrangement of apparatus suitable for carrying out our process. It is to be understood, however, that the invention may be otherwise embodied or practiced within the Vsco of the following claims.

We claim:

1. The process of making chemically pure benzene, which comprises subjecting industrial pure benzene having a boiling range of V'11.5 C. to'

82.5 C. tofractional crystallization by freezing while agitated to crystalline benzene and remove lower freezing point impurities therefrom.

zene, which comprises subjecting industrial pure benzene having a boiling range of '17.5 C. to 82.5 C. to fractional crystallization by freezing while agitated with ainto c benzene and rerystalline move lower freezing point impurities therefrom.

3. The processof making chemically pure ben# zene, which comprises subjecting industrial pure v nene,'which comprises subjecting industrial pure bennene having a boiling range of '19.5 C. to 81.5

C. to fractional crystallization by freezing while' yagitated with air to crystalline benzene and remove lower freening point impurities therefrom.

5. 'Iheprocessofmakingchemicallypurebennene, which comprises subjecting industrial pure benzene to fractionalcrystallization by freezing atanaverage'ratenottoexceed5% perhour during the freezing periodY while agitated toA crystalline benzene and remove lower freezing point impurities therefrom.

6. Theprocessofmakingchemicallypurebenzene, which comprises subjecting industrial pure benzene to fractional crystallization by freezing atanavera'gerate'nottoexceedl, perhour during the freezing period while agitated with air to crystalline benzene and removelower freenlng point impurities therefrom.

'1. Theprocess of making chemically pure bennene, which 'comprises subjecting industrial pure benncne havinga boiling range of '19.5 C. to 81.5 C.tofractionalcrystallizationbyfreeaingatan averageratenottoexceedfit pcrhourduring the freezing period whileragitated with-airY to crystalline bennene and remove lower freezing point impurities therefrom.

8. The process'of beh.- -zene, which comprisessubjecting a-light oil distillate containingatleast90% pure benzene to fractional crystallization byfreening while agi tated to crystalline benzene and remove lower freesingpointimpuritiestherefrom.

9.1heprocessofmaking n ene,whichcomprlses Mmmm-bem.

bennenetofractinnalcrystallinationbyfreesing 1 while agitated to form a solidified body of chemically pure benzene having a liquid core contain-i ingcimpurities, draining on the liquid, and thereafter removing the benzene.

a 10. The process of making chemically pure benzene, which comprises subjecting industrial pure benzene to fractional crystallization .by freezing while agitated to form a solidified body of chemically pure benzene having a. liquid corel containing impurities, draining off the liquid, and thereafter melting 'and drawing oif the bennene.

11. The process of, making chemicallypure benzene, which comprises subjecting industrial pure benzenev to fractional crystallization by freezing while agitated with air to form a solidified body of chemically pure benzene having a i liquid core containing impurities, draining off 2. Theprocessofmakingchemically'pureben;z

the liquid, and thereafter removing the benzene.

'12. The process of making chemically pure benzene, which comprises subjecting industrial pure benzene having a boiling range of 77.5 `C. to 82.5 C. to fractional crystallization by freezing while agitated with air zo form a sonained body y of chemically pure benzene having a liquid core containing' impurities, draining olf the liquid, and thereafter melting and drawing off the ben- 13. The process benzene, which comprises subjecting industrial pure benzene to fractional crystallization by hour vduring-the freezing period while agitated to form a solidified body'of chemically pure bennene having a liquid core containing impurities, draining oi! the liquid, and thereafter removing the benzene. v

14. The process of making chemically pure benzene, which comprises subjecting industrial .pure benzene to fractional crystallizationby freezing at a rate not to exceed'5% per hour to form a solidified body of chemicallypure ben Vof .making chemically pu're' 'freezing at an average rate not to exceed 5% per nenevhaving aliquid core containing impurities,

drainingoff the liquid, and thereafter removing 16. The process of niaking chemically pure bennene, which comprises subjecting industrial pure benzene having a boiling range of '19.5" C. to 81.5 C. to fractionalA crystallization by freezing at a rate not to exceed 5% per hourto form a solidified body of chemically pure benzene having a liquid'core containing impurities, draining olf thev liquid, and thereafter removing the bennene. ROBERT .W.v CAMPBELL.

FRED W. WAGNER. 

